556 
R. RUGGLES GATES AND NESTA THOMAS. 
particularly clearly drawn. And in the light of these facts 
we are forced to contrast sharply the ordinary hybrid 
behaviour, in which the cliaracters contained in the parents 
reappear in the offspring in various re-combinations and 
blends, with mutations, in which a germinal change occurs, 
leading, as with Galton^s polyhedron, to a new condition of 
stability in the organism. Tetraploidy and the presence of 
the extra chromosome are both cases in which the occurrence 
of such germinal changes is proven beyond doubt. 
Obviously, then, tetraploidy and the occurrence of mutants 
with an extra chromosome are both processes which are not 
Mendelian in character, and they are of much importance at 
the present time as proving cytologically the essential correct- 
ness of the conception of germinal changes or mutations. 
When only the external characters are considered, it may be 
diflBcult or impossible to prove with any finality that the new 
characters are really progressive or that they do not repre- 
sent merely recombinations of previous characters. But the 
nuclear structure furnishes incontrovertible evidence. 
In conclusion, we are indebted to Prof. J. B. Farmer, 
F.R.S., for the examination of a number of our critical 
preparations. 
Summary. 
This paper contains a study of the lata and semilata 
series of mutations in CEnothera. Twenty-one such plants 
in cultures from various sources were examined and 15 
chromosomes have been found in every case, though the 
mutants were derived from 14-chromosome races. The races 
in question were from such diverse sources as Sweden, 
Hungary, Madrid, Birkenhead, the cultures of de Vries, and 
the oftspring of certain hybrids. 
Especial interest attaches to a 15-chromosome mutant called 
(E. lata rubricalyx, which appeared in the Eg of CE. mut. 
rubricalyx x (E . grandiflora, and which combined the 
foliage and habit of lata with red pigmentation inherited from 
rubricalyx. Similarly the race of OE. biennis L. from 
